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  <section id="cmake-ninja-output-path-prefix">
<span id="variable:CMAKE_NINJA_OUTPUT_PATH_PREFIX"></span><h1>CMAKE_NINJA_OUTPUT_PATH_PREFIX<a class="headerlink" href="#cmake-ninja-output-path-prefix" title="Link to this heading">¶</a></h1>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.6.</span></p>
</div>
<p>Tell the <a class="reference internal" href="../manual/cmake-generators.7.html#ninja-generators"><span class="std std-ref">Ninja Generators</span></a> to add a prefix to every output path in
<code class="docutils literal notranslate"><span class="pre">build.ninja</span></code>.  A trailing slash is appended to the prefix, if missing.</p>
<p>This is useful when the generated ninja file is meant to be embedded as a
<code class="docutils literal notranslate"><span class="pre">subninja</span></code> file into a <em>super</em> ninja project.  For example, the command:</p>
<div class="highlight-shell notranslate"><div class="highlight"><pre><span></span><span class="nb">cd</span><span class="w"> </span>super-build-dir<span class="w"> </span><span class="o">&amp;&amp;</span>
cmake<span class="w"> </span>-G<span class="w"> </span>Ninja<span class="w"> </span>-S<span class="w"> </span>/path/to/src<span class="w"> </span>-B<span class="w"> </span>sub<span class="w"> </span>-DCMAKE_NINJA_OUTPUT_PATH_PREFIX<span class="o">=</span>sub/
<span class="c1">#                                 ^^^---------- these match -----------^^^</span>
</pre></div>
</div>
<p>generates a build directory with its top-level (<span class="target" id="index-0-variable:CMAKE_BINARY_DIR"></span><a class="reference internal" href="CMAKE_BINARY_DIR.html#variable:CMAKE_BINARY_DIR" title="CMAKE_BINARY_DIR"><code class="xref cmake cmake-variable docutils literal notranslate"><span class="pre">CMAKE_BINARY_DIR</span></code></a>)
in <code class="docutils literal notranslate"><span class="pre">super-build-dir/sub</span></code>.  The path to the build directory ends in the
output path prefix.  This makes it suitable for use in a separately-written
<code class="docutils literal notranslate"><span class="pre">super-build-dir/build.ninja</span></code> file with a directive like this:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>subninja sub/build.ninja
</pre></div>
</div>
<p>The <code class="docutils literal notranslate"><span class="pre">auto-regeneration</span></code> rule in <code class="docutils literal notranslate"><span class="pre">super-build-dir/build.ninja</span></code> must
have an order-only dependency on <code class="docutils literal notranslate"><span class="pre">sub/build.ninja</span></code>.</p>
<div class="versionadded">
<p><span class="versionmodified added">Added in version 3.27: </span>The <span class="target" id="index-0-generator:Ninja Multi-Config"></span><a class="reference internal" href="../generator/Ninja%20Multi-Config.html#generator:Ninja Multi-Config" title="Ninja Multi-Config"><code class="xref cmake cmake-generator docutils literal notranslate"><span class="pre">Ninja</span> <span class="pre">Multi-Config</span></code></a> generator supports this variable.</p>
</div>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>When <code class="docutils literal notranslate"><span class="pre">CMAKE_NINJA_OUTPUT_PATH_PREFIX</span></code> is set, the project generated
by CMake cannot be used as a standalone project.  No default targets
are specified.</p>
<p>The value of <code class="docutils literal notranslate"><span class="pre">CMAKE_NINJA_OUTPUT_PATH_PREFIX</span></code> must match one or more
path components at the <em>end</em> of <span class="target" id="index-1-variable:CMAKE_BINARY_DIR"></span><a class="reference internal" href="CMAKE_BINARY_DIR.html#variable:CMAKE_BINARY_DIR" title="CMAKE_BINARY_DIR"><code class="xref cmake cmake-variable docutils literal notranslate"><span class="pre">CMAKE_BINARY_DIR</span></code></a>, or the
behavior is undefined.  However, this requirement is not checked
automatically.</p>
</div>
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